1. Field of the Invention
The present invention relates to a toner for use in electrophotography. In addition, the present invention also relates to a developer, an image forming method, an image forming apparatus, and a process cartridge using the toner.
2. Discussion of the Background
For the purpose of improving quality of electrophotographic images, recently toners are being modified to have a smaller particle diameter. The smaller particle diameter a toner has, the lower fluidity the toner has. When a toner has poor fluidity, the toner tends to aggregate and transferability thereof deteriorates. As a result, hollow defects tend to occur in the resultant image. In particular, this phenomenon notably occurs in a toner including a release agent (such as a wax) so as to prevent occurrence of a paper winding problem and an offset problem. The paper winding problem is a phenomenon in which a transfer medium having a toner image thereon is wound around a fixing member or gets stuck to a separation pick, due to adhesion of the toner image thereto. The offset problem is a phenomenon in which a part of a fused toner image is adhered and transferred to the surface of a fixing member, and then the part of the toner image is re-transferred to an undesired portion of a transfer medium. Deterioration of transferability notably occurs in toners for use in full-color image forming apparatuses.
When fluidity of a toner decreases, the occurrence of contact with a charge giving member (such as a carrier) decreases, and therefore the toner cannot be evenly charged. As a result, background fouling tends to occur in the resultant image. In particular, this phenomenon notably occurs in a toner including a release agent (such as a wax). Background fouling is a phenomenon in which the background portion of an image is soiled with toner particles which are not sufficiently charged, at a time when an electrostatic latent image formed on a photoreceptor is developed with a toner. Deterioration of chargeability notably occurs in toners for use in full-color image forming apparatuses.
In attempting to solve these problems, published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2001-154457 discloses an image forming apparatus including a combination of a magnetic brush formed of magnetic particles having a volume resistivity of from 104 to 109 Ω·cm and a toner having an acid value of from 3 to 40 mgKOH/g. It is described therein that such an image forming apparatus hardly produces abnormal images such as toner scattering and fogging.
JP-A 2003-29467 discloses a developer including a carrier of which a cover layer includes an oxime group in an amount of from 0.1 to 200 ppm based on total weight of the cover layer, and a toner having an acid value of from 5 to 50 mgKOH/g. It is described therein that such a developer can produce high quality images for a long period of the time.
However, these attempts are insufficient to prevent deterioration of transferability, when a multiple toner image formed on an intermediate transfer medium is transferred on a transfer medium in a full-color image forming apparatus.
On the other hand, in order to increase fluidity of a toner, a method in which the added amount of an external additive (such as silica) is increased is known. However, chargeability of the resultant toner changes with long-term use, resulting in the occurrence of background fouling. When the added amount of an external additive is too large, the external additive tends to migrate to the surface of a photoreceptor. A toner also tends to accumulate on the surface of the photoreceptor, while the external additive serves as a core. As a result, image noises such as black spots tend to occur in the image produced.